In 1965, the strung surface of most tennis rackets had remained unchanged for many years, and rarely exceeded 451 cm.sup.2. However, since 1970, the use of metal and above all of plastic materials reinforced with glass fibers and sometimes with carbon, boron, or ceramic fibers, has made it possible to manufacture large-size frames with strung surfaces of as much as 680 cm.sup.2, i.e., more than 50% greater than the usual conventional surface of 451 cm.sup.2, and having a more or less oval shape with a long axis which is sometimes more than 34 cm long and with a short axis which may be more than 26 cm long. Such rackets are described in U.S. Pat. No. 3,999,756.
With such strung surfaces, the lengths of the main strings and of the cross strings are naturally increased. This gives rise to improved resilience of the stringing as a whole and an increase in the size of the zone in which said resilience gives rise to high energy restitution.
With a large-size racket weighing less than 340 grams, it is possible to impart nearly as much speed to a ball as when using a racket having a strung area of 451 cm.sup.2 and a weight of 375 g.
Many beginners, older players, and players who play tennis only occasionally, greatly appreciate such rackets which require little force for obtaining a satisfactory result.
However, other players, in particular the best players, consider that the large size of the frame increases the aerodynamic drag of the racket and makes it more difficult to handle, in particular hindering the quick movement required for return of service.
Further, when the speed of play is due above all to the high resilience of the strings of large-size rackets, it is not possible to obtain adequate accuracy and control.
In any event, all players appreciate the advantages of rackets having an area of more than 451 cm.sup.2, but many rackets currently being manufactured have a strung area of less than 590 cm.sup.2. The best players often use rackets with an area of about 570 cm.sup.2 only.
With such rackets, it is possible to obtain good restitution of energy and good accuracy when the ball is struck at points near the center of the strung surface, where both the main and the cross strings are longest.
Studies of string wear and experiments performed with stroboscopic and electronic equipment have shown that most players generally manage to strike the ball at points close to the X axis of symmetry of the frame.
But specially when trying to return services--which are becoming faster and faster with servers taller and stronger than in the past--even the best players do not have enough time to execute a full swing and to change their body, arm, and hand actions to avoid striking the ball at points distant from axis Y, perpendicular to axis X. With a short swing, the player must rely on the resilience of the strings. But, with impact points spaced from axis Y, the length of cross strings is shorter than in the center of the strung surface and in one direction, there is less than half the main string length between impact points and the frame. Impacts at such points result in poor restitution of energy and accuracy.
When serving, many players, deliberately or instinctively, strike the ball at points as far as possible from the end of the handle, producing poorer restitution of energy with shorter string length, as above explained.